The present invention relates to a phase displacement device for displacing the angle of rotation of a camshaft in relation to the angle of rotation of a crankshaft.
In internal combustion engines, the crankshaft drives one or more camshafts via a primary drive formed for example as a toothed belt. For this purpose, a camshaft wheel is fastened on each camshaft via which the primary drive drives the camshaft. At each point in time, there takes place a geared conversion of the angle of rotation of the crankshaft, such that an angle of rotation φK of the crankshaft of 720° is converted into an angle of rotation φN of the camshaft of 360°. The ratio of the two angles of rotation is constant through this coupling. In most applications, this fixed coupling between the camshaft and the crankshaft has a ratio of:φN(t)/φK(t)=2.
However, the operating characteristics of an internal combustion engine can be optimized, in particular with respect to fuel consumption, the emission of exhaust gases, and smooth running performance, if the system, coupled via the primary drive, between the camshaft and the crankshaft can be modified, thus displacing the phase between the two shafts.
In DE 100 38 354 A1, in order to sense the phase displacement, sensor devices are attached to the camshaft and the crankshaft or to the camshaft wheel; these sensor devices sense the actual position of the camshaft in relation to the actual position of the crankshaft or of the camshaft wheel, and from this the positions, or also the rotational speeds, of the shafts can be determined. Such a sensor device can for example be realized by Hall sensors that operate in contactless fashion.
A disadvantage of such a design is that discrete angular marks must be attached to the camshaft and to the crankshaft which can then be picked up by the sensors. The number of these angular marks on the camshaft is dependent on the number of cylinders or on the periodic camshaft moment of alternation. Because it is not possible to place arbitrarily many angular marks on the camshaft, the measurement precision of the position acquisition is dependent on the space between adjacent angular marks. The longer the time interval required for the sensing of two adjacent angular marks, the more imprecise the measurement result is; i.e., the phase displacement cannot be determined precisely.